1. Field of the Invention
The present invention relates to an ion chromatography system for conducting an environmental analysis in semiconductor equipment and, more particularly, to a pretreatment section of such an ion chromatography system which can prepare and treat a sample efficiently and adequately.
2. Description of the Related Art
Manufacturing a semiconductor device requires precise processing technologies and a clean environment. It is necessary, therefore, to install special equipment for providing a clean environment such as a clean room in a semiconductor manufacturing facility. An exhaust system must also be arranged for removing foreign materials and particles from the environment of the facility. Various methods are used to check the environment in the clean room with the aim of ensuring that the level of the foreign materials is normal.
In such a semiconductor manufacturing facility, one known method of controlling the foreign materials in the atmosphere is the ion chromatographic method. In this method, air collected at a target position is passed through an absorbent solution such as pure water contained in a vessel of an impinger device, and ions of gas components dissolved in the absorbent solution are assayed using ion chromatography to check whether foreign materials are present in the atmosphere.
FIG. 1 is a schematic diagram of a conventional ion chromatography system. The ion chromatography system can precisely detect microscopic components of a sample by using the electric conductivity of ions in a medium such as pure water. Referring to FIG. 1, a separation device (not shown) first divides a sample from the sample feed inlet 14 into anionic and cationic portions. For each side of the apparatus shown in FIG. 1, sample feed control valve 11, which is regulated by an operator, directs the ion-separated sample to a sample loop 12, or directly to a discharge line 13. In a similar way, a carrier solvent used in the ion chromatography system is directed to a sample loop 12, or to the discharge line 13, or directly to a guard column 16 by a carrier solvent control valve 15. A part of the sample having a stronger affinity to the substances in the guard column 16 passes to a separation column 17 to carry the sample to a detector 18 based on the difference in the moving velocities of the substances.
In another ion chromatography system, a concentration column is used instead of the sample loop for analyzing highly pure water so that a concentrated sample is carried to a guard column, or an original sample is directly transported to the guard column by using an injector.
Because the ion chromatography system is an analytical instrument which detects the electrical conductivities of ions in a liquid phase, its ability to analyze for microscopic components of the atmosphere is limited.
Two type of methods are used in the preparation of a sample of atmosphere: a simple method and an atmospheric pressure transporting method.
In the simple type method, an absorbent solution contained in a vessel having a wide opening is placed at a desired position for a designated time period in order for the atmosphere at that position to naturally dissolve in the absorbent solution.
FIG. 2 shows a conventional impinger device is used for carrying out the atmospheric pressure transporting type method of preparing a sample. An absorbent solution vessel having the shape of a barrel is partially filled with an absorbent solution 22. An inlet of the vessel 21 is closed with a seal 23 through which suction and exhaust pipes 24 and 25 pass. The suction pipe 24 is used to suction the atmosphere into the absorbent solution 22. The atmosphere, having passed through the absorbent solution 22 into the space above the solution, is discharged to the outdoors through the exhaust pipe 25. A pump 26 is installed in at least one of the two pipes so that the atmosphere outside the vessel can pass through the absorbent solution in order for soluble components of the atmosphere to be dissolved in the solution.
In both methods, a sample is prepared from the atmosphere collected at a desired position and carried into the analytical equipment. The conventional methods for analyzing the components of the atmosphere using the impinger device and ion chromatography system have some disadvantages.
First, the sampling point, where the atmosphere is collected and a sample is prepared, is not identical to the position where the analytical equipment actually carries out its analysis. External contaminants may be introduced in the sample while the sample is carried to the equipment and injected into it. The contaminants on the glass sample vessel may also be dissolved in the sample.
Secondly, proper measures cannot be taken immediately if an unexpected situation-occurs at the sampling point due to the time required for carrying the sample and injecting it into the equipment.
In addition, the conventional impinger device uses pipes for carrying the sampled atmosphere into the absorbent solution under pressure. This piping decreases the surface area of the atmosphere which is allowed to contact the solution, thereby lowering the absorption efficiency of the atmosphere components. Excessive time is thus required to dissolve soluble components in the absorbent solution.